FIG. 8 shows a semiconductor device described in Japanese Patent Laying-Open Gazette No. 7-250485. The semiconductor device shown in FIG. 8 is a perspective view showing a module (Intelligent Power Module: hereinafter abbreviated as IPM) 80 storing power devices and an IC-ed control device controlling these power devices in a single package.
Referring to FIG. 8, the IPM 80 comprises a control IC 2100 which is an IC-ed control circuit and power chips 2200 which are power devices in an upper package OP10. The control IC 2100 and the power chips 2200 are electrically connected with control terminals TM10 and main circuit terminals TM20 respectively in the package. The upper package OP10 and a package base BP10 are formed by molding, and resin, such as epoxy resin, for example, is the main component thereof.
FIG. 9 shows a plan perspective view and a sectional view in case of observing the IPM 80 from the side of the upper package OP10 (upper surface side).
As shown in FIG. 9, the control IC 2100 is electrically connected with the control terminals TM10 through gold wires W20, and the power chips 2200 are electrically connected with the main circuit terminals TM20 through aluminum wires W10.
At this point, the main circuit terminals TM20 have functions for serving not only as terminals but also as die pads for mounting the control IC 2100 and the power chips 2200. A heat sink HP is arranged on lower portions of the control terminals TM10 and the main circuit terminals TM20, to be in a structure of radiating heat generated by the power chips 2200 in a device operation through the heat sink HP.
A fabrication process for the IPM 80 of such a structure is first adapted to prepare a lead frame which is one of elements forming the IPM 80, for die-bonding the control IC 2100 and the power chips 2200 to prescribed positions of this lead frame. The process is then adapted to connect the control IC 2100 and the control terminals TM10 with each other through the gold wires W20 and to connect the power chips 2200 and the main circuit terminals TM20 with each other through the aluminum wires W10, thereby completing packaging on the lead frame. At this point, the diameter of the gold wires W20 is about 30 .mu.m, and the diameter of the aluminum wires W10 is about 300 .mu.m.
Then, the IPM 80 is completed by performing transfer molding in a state mounting the aforementioned packaged lead frame on the heat sink HP.
The transfer molding is a method of performing forming of resin by holding the packaged lead frame with upper and lower molds and press-fitting plastified (plastification) thermosetting resin (hereinafter referred to as mold resin) into cavities of these molds. At this point, the gold wires W20 are thinner than the aluminum wires W10 as described above, and hence deformation and breakage of the gold wires such as wire deformation in which the shape of the gold wires W20 is lost by press fitting of mold resin, a wire touch in which adjacent gold wires W20 come into contact with each other and wire disconnection in which the gold wires W20 are broken may take place.
In particular, enlargement of an IPM recently progresses and the volume of a package part is also in a tendency to enlarge. Since advancement of an injection speed is now being required in view of improvement of productivity, prevention of the phenomena described above is an important subject.
A method generally employed in order to prevent the aforementioned phenomena is a method of coating a region where gold wires are employed, i.e., a placed region of a control IC by employing resin such as polyimide, for example, in advance of transfer molding. Namely, a region X to which hatching is applied is the object region, when describing with reference to FIG. 9.
Thus, in the conventional IPM, there has been such problems that it is necessary to coat the region where gold wires are employed in advance of transfer molding in order to prevent deformation and breakage of the gold wires in press fitting of resin, the number of fabrication steps increases, and the fabrication cost increases.